Dissociation of plaque formation from glucan-induced agglutination in mutants of Streptococcus mutans

The traits adhesion and cohesion are manifested in Streptococcus mutans by in vitro plaque formation and glucan-mediated agglutination and have been dissociated in mutants of this caries-associated microbe. In these mutants, which differ from each other in colonial morphology, we have observed a consistent loss of ability to form adhesive microbial deposits (plaque) on wires, but only a minimal alteration from the wild type in ability to agglutinate into macroscopic clumps in the presence of exogenous glucans or sucrose. Also, when these mutants were cultured in sucrose-containing medium, there was an increase in the synthesis of water-soluble, extracellular glucans and a decrease in the synthesis of alkali-soluble, cell-associated glucans. Based on these findings, it appears (i) that in vitro plaque formation and agglutination are distinct and dissociable traits, and (ii) that adhesion but not agglutination appears related to the synthesis of alkali-soluble, cell-associated glucans.